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87

This depends on how much thrust you have available. With enough thrust, you don't need to be in Earth orbit at all: you can launch straight into an escape trajectory. New Horizons did this, more or less: after launch it did about 1/4 orbit before the second stage was ignited again and insertion into its trajectory towards Jupiter began. With very little ...


70

Yet surely nobody would classify Neil Armstrong's lunar bunny-hops as suborbital spaceflights. Why not? There's no essential difference between a high-eccentricity trajectory with an apolune of 1 meter and one with an apolune of 100 kilometers. How would you define the space boundary on these planets? If the body doesn't have an atmosphere dense ...


66

The term for orbits in our solar system around the Sun is Heliocentric. Closed Heliocentric Orbit The solar observation probe Ulysses is the furthest artificial satellite around the sun. It's in a highly inclined, elliptical orbit ranging from 1.35 Astronomical Units (AU) to 5.4 AU. It was a joint project by ESA/NASA launched in 1990 and decommissioned in ...


64

Primarily, because without a lot of extra equipment, they could at best be space coffins for the astronauts. First, they share life support with the rest of the station. Air circulated through them is scrubbed of CO2 in the station's scrubbers. Heat is regulated through station's radiators. This all is powered by station's solar panels. And that's just for ...


58

The instability in orbits of our artificial satellites come from a few basic causes: Atmospheric drag and solar wind effects The Earth isn't a perfect uniform sphere but is slightly lumpy, which means its gravitational field isn't uniform Other massive objects in the solar system perturb their orbits with their gravity So let's consider them one by one. ...


53

The decision to orbit (and assemble) the International Space Station (ISS) in 51.65° prograde Low Earth Orbit (LEO) was driven by its accessibility and utility. You see, inclination changes are terribly expensive for visiting spacecraft delivering astronauts / cosmonauts, consumables, science experiments and other cargo, and ideally, you'd always launch ...


46

Zero See at: https://en.wikipedia.org/wiki/Escape_velocity for theory. Once you build enough velocity to surpass gravitational attraction, you will leave planetary orbit. A spacecraft simply circling the earth in orbit is not inherently doing anything to contribute to escaping that orbit.


43

Essentially, this is a result of observational bias. A natural satellite will only orbit a parent for extended time periods precisely because the orbit it is in is stable †. The plain truth of the matter is that we are simply injecting satellites into unstable orbits. If you were to move natural satellites into the same orbits, they'd be unstable too. ...


41

Statement of the Problem The problem you want to solve is called the Kepler problem. In your formulation of the problem, you're starting out with the Cartesian orbital state vectors (also called Cartesian elements): that is, the initial position and velocity. As you have discovered, the only way to propagate the Cartesian elements forward in time is by ...


40

I treated this as a problem of geometry and came up with this: The sun is the large yellow disk. The earth is the largest black disk, obscuring most of the sun The left-hand dark-grey disk is the moon as it transits across the near-side of the earth, with respect to L2. In reality in this position, the disk of the moon would appear completely black. I ...


37

Retrograde orbits have multiple use-cases. First of all you should note that "retrograde" doesn't mean 180° inclination - everything > 90° is considered retrograde. This places all sun-synchronous satellites which operate at about 98° inclination in retrograde orbits. The usefulness of sun-synchronous orbits should be obvious. Retrograde orbits of course ...


36

I understand the reasons behind each of this manouveurs, however I'm wondering if this is how real rockets get into orbit. Cutting off the engine and letting the rocket loose vertical speed looks counter-intuitive to me (you basically spend a lot of fuel to accelerate and then you let the rocket slow down). In most real launches to low Earth orbit, the ...


33

This mission study came up with a 900 kg nuclear-electric-propulsion spacecraft launched on an Ariane V with a C3 of 100 and a Jupiter gravity assist along the way. 1.05 kW electrical power at Pluto from RTGs is required. That would be four "classic" NASA RTGs, or about nine MMRTGs. It has a 20 kg science payload. (New Horizons has ~30 kg of instruments, ...


33

Ultimately, "the edge of space" is an agreed upon convention. In other words it is essentially arbitrary, something which only humans even care about (well maybe space aliens too <grin>). Yes, there are various physical properties which can be used to define this boundary and the measurements themselves are not arbitrary, none-the-less, the choice of ...


33

Physics In regards to the physics, KSP is fairly realistic, other than it not modeling n-body physics (which isn't really relevant in scope of orbiting Earth/Kerbin). In regards to the engineering, KSP makes its parts much stronger than the real life components. The tradeoff here is that when something finally breaks in KSP, it explodes and disappears. ...


32

You're confusing units. The maximum speed of the X-15 was 7274 km/h, or about 2 km/s. Orbital speed is around 8 km/s. The X-15 didn't carry enough fuel to reach orbital speed.


31

As Undo mentioned, the type of orbit is called a retrograde. A pure retrograde orbit is quite rare, in fact, NORAD currently isn't tracking any (unclassified) objects with a 180 inclination (Pure Retrograde). However, there are a fair number of satellites with a retrograde inclination (Over 90 degrees). Of particular note is the Sun Synchronous orbits of ...


31

This was one of the questions just now during the Rosetta press briefing. This video was shown during the presentation: The triangular trajectory are hyperbolic orbits with respect to the comet and they'll (also, among other tasks also mentioned in the image you're attaching) serve to establish its mass. In essence ...


30

By convention the altitude of a spacecraft is the distance to the center of the Earth minus roughly 6378 kilometers, or some reference radius that is representative of the equatorial radius of the Earth. Spacecraft altitude is not really used as a precise description of a satellite's position, since its only a scalar and it requires a definition, but if you ...


30

Twelve Apollo astronauts landed on and walked on the Moon Twelve more Apollo astronauts orbited the Moon without landing So that's twenty-four individuals that count towards "(except for the moon of course in the '60s/'70s)" Incidentally, as @ takintoolong just pointed out, the answer to Which astronaut travelled farthest from Earth? is the Apollo 13 crew. ...


27

This is a great question. I wanted to provide an answer which cited some specific, real-world situations. Currently the only people in space are those aboard the International Space Station. If anyone could potentially get into a scenario as you describe in your question, it would be them. Currently, on spacewalks, a huge number of safety procedures are ...


27

Is the orbit shown in the graphic wrong, or is my understanding of orbital mechanics lacking, having only been influenced by KSP? It's not an either-or question. The graphic is "wrong" from the perspective of an Earth-centered inertial frame. That graphic instead uses a synodic frame, a frame that rotates with the Earth's orbit about the Sun. You can tell ...


26

The answer is "yes", and there are a surprising number of ways to argue this. You will probably want to look at the question about small orbits around black holes in Physics Stack Exchange. At sufficient distances, black holes are not special Black holes behave the same as any other spherical collection of matter. This is a conclusion of the (...


26

As noted by Mys_721tx in comments, this is the trajectory of the object J002E3 -- believed to be the S-IVB upper stage launched with the Apollo 12 mission -- and the animation is accurate. As David Hammen explains in his (better) answer, the animation is showing a rotating frame of reference centered on the Earth. Because of the rotation, and the fact that ...


26

I'm afraid you are incorrect. An object on the equator of Earth has a velocity of ~460 m/s. A satellite in geosynchronous orbit has a velocity of ~3000 m/s. You may be confused by the fact that both objects complete an "orbit" in 24 hours. But consider the fact that the satellite travels a significantly greater distance in that time.


26

The UCS has a list of satellites which can be sorted by launch mass. The top 10 is mostly spy satellites for which it's difficult to determine if they're active or defunct. The heaviest satellite of which I'm sure it's not functional, is Envisat at 8 tons. (1:1 model of Envisat at Space Expo in Noordwijk, the Netherlands) This list doesn't account ...


25

The main reason they are in such a high orbit is to allow for more of the Earth to be visible at any one time. In order to have a reasonable amount of the Earth visible, you have to be high up. A lower altitude could in theory work as well, but the chosen altitude seems to be a far enough distance to be useful, but not so far as to have communication link ...


25

Launching a rocket into space is really all about getting horizontal velocity: If you go fast enough sideways, you miss the Earth when you fall towards it and stay in a perpetual free fall. That is an orbit. You are correct that a spacecraft is initially launched in a vertical position, but it later turns to gain velocity sideways. And a lot is needed as ...


25

It is axiomatic that satellites in the same orbit travel at the same speed. Your axiom is not axiomatic. The idea that there is something called an "orbit" that a satellite can be "in" is a simplification, just like cars are in lanes. They are, roughly, most of the time, but in many countries they are all over the place, without discrete "lanes" evident ...


24

Think of this as a slightly different question, and the answer becomes more clear. How many times do you have to circle the Sun to leave orbit? The Earth has been orbiting our Sun for about 4.5 Billion years with each year being one orbit. The Earth is expected to stay in orbit around the Sun for the next few billion years. Also consider the moon has ...


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